1. Field of the Invention
The present invention relates to an optical disk apparatus which records information by irradiating a laser beam onto an optical disk medium, and a method for setting its control parameters.
2. Description of the Related Art
In recent years, optical apparatuses have been extensively developed as means for recording/reproducing large-capacity data, and there has been an approach to achieving a higher recording density. One example of them is a phase-change type optical disk apparatus utilizing reversible state changes between a crystal state and an amorphous state.
In a phase-change type optical disk apparatus, a semiconductor laser beam having two powers (a peak power which makes a crystal portion amorphous and a bias power which crystallizes an amorphous portion) is irradiated onto an optical disk medium, whereby marks (amorphous portions) and spaces (crystal portions) interposed between the marks are formed on the optical disk medium.
The marks and spaces have different reflectivity, so that a recorded signal is read by utilizing the difference in reflectivity during reproduction.
Herein, a signal is recorded at one recording focus position (irradiation spot position of a laser beam), and the signal is reproduced at one reproduction focus position (irradiation spot position of a laser beam). A series of steps for determining the quality of a reproduction signal by a quality determination circuit will be described by using a path on a recorded track of irradiation spots of a semiconductor laser beam.
Actually, a track is moved into an irradiation spot by the rotation of a disk. However, for simplicity, it is assumed that an irradiation spot moves onto a recording track.
FIG. 65 is a view showing a track structure of a conventional optical disk 26. Reference numeral 27 denotes a groove track formed in the shape of a spiral. In this figure, recording from a point 21 to a point 22 is performed clockwise at one recording focus position. Then, in order to reproduce a signal, for example, an irradiation spot jumps from a point 23 to an inner track, passing through a point 24, and starts moving on a track from a point 25. Then, the irradiation spot moves clockwise on a track from the point 25 to the point 21, and reproduces a signal previously recorded from the point 21, whereby the quality determination circuit determines the quality of a reproduction signal.
In the case of obtaining an optimum recording focus position, a recording focus position is gradually changed, and every time the recording focus position is changed, the above-mentioned recording and reproduction are repeated. Thus, a recording focus position at which a reproduction signal of the highest quality is obtained is determined.
Similarly, in the case of obtaining an optimum reproduction focus position, a reproduction focus position is gradually changed, and every time the reproduction focus position is changed, the above-mentioned recording and reproduction are repeated. Thus, a reproduction focus position at which a reproduction signal of the highest quality is obtained is determined.
In the case of setting a tilt angle (i.e., an incident angle of a laser beam with respect to an optical disk), the tilt angle is gradually changed, and every time the tilt angle is changed, the above-mentioned recording and reproduction are repeated. Thus, a tilt angle at which a reproduction signal of the highest quality is obtained is determined.
An example of a method for obtaining an optimum irradiation power of a semiconductor laser beam is described in, for example, Japanese Laid-open Publication No. 4-141827. According to this method, a signal is recorded while a peak power is gradually decreased from the high power side, for example, under the condition that a bias power is fixed. In this case, every time a signal is recorded with one peak power, the signal is reproduced with a reproduction power, and a quality determination circuit determines the quality of a reproduction signal. Then, a lower limit value of a power which the quality determination circuit determines is “good” is obtained, and a margin value is added to the lower limit value, whereby an optimum power is set.
In the above-mentioned case, recording and reproduction of a signal are required to be repeated with respect to a track in accordance with the process shown in FIG. 65 in the same way as in obtaining recording and reproduction focus positions, and a tilt angle.
On the other hand, as recording pits are recorded with a higher density, there arise problems such as a decrease in S/N and a waveform interference between the recording pits in reproducing a recorded signal, or changes in characteristics of a reproduction channel caused by the variation of optical disk media and optical disk apparatuses. Thus, there has been a demand for an apparatus in which an increase in error rate due to this problem is small.
In order to overcome the problem of the changes in characteristics of a reproduction channel, a method for optimizing an equalizer characteristic in each disk has been considered.
For example, parameters of an equalizer characteristic are set to be the largest boost amount and a frequency at which a boost amount becomes maximum. Under the condition that the frequency at which the boost amount becomes maximum is fixed, a recorded signal is reproduced while the boost amount is gradually increased from the lower side. Thus, the quality of a reproduction signal is detected, and the boost amount at which the best quality reproduction signal is obtained, is set as the optimum boost amount. Then, while the boost amount is fixed, a frequency at which the boost amount becomes maximum is similarly obtained.
Herein, in the same way as in obtaining recording and reproduction focus positions, and a tilt angle, recording and reproduction of a signal are required to be repeated with respect to a track in accordance with the process shown in FIG. 65, whereby an equalizer characteristic is optimized.
The above-mentioned conventional optical disk apparatus is predicated on optical disks in which a groove-shaped track (groove track) is formed in the shape of a spiral, and a recording area is provided in either the groove track or the land track (i.e., track between the grooves), and an optimum focus position, an optimum tilt angle, etc. are obtained with respect to this type of optical disk. However, optical disks in which a signal is recorded in both the land track and the groove track are not considered.
The land track and the groove track have different physical properties such as the shape of a groove and reflectivity due to the difference in arrangement, and an optimum focus position, an optimum tilt angle, etc. are different with respect to each track. Therefore, in the case of performing recording and reproduction with respect to both the land track and the groove track, an optimum focus position, an optimum tilt angle, etc. are required to be set for the land track and the groove track, respectively. Alternatively, an average of an optimum focus position, an average of an optimum tilt angle, etc. are required to be set for the land track and the groove track, respectively. However, in both the cases, recording and reproduction of a track are required to be repeated by the process shown in FIG. 65 for the land track and the groove track, separately. Therefore, in the case of performing recording and reproduction using both the land track and the groove track, a longer time and more effort is required compared with the case of using only one of either the groove track or the land track.
Specifically, a waiting time for rotation (point 23→point 24→point 25→point 21) in FIG. 65 is used for the land track and the groove track, respectively, which decreases an efficiency.
The similar problem is caused in obtaining and setting an optimum power, an optimum equalizer characteristic, as well as an optimum focus position and an optimum tilt angle. Thus, a longer time and more effort are required.